Node.js, Express.js & MongoDB Interview Cheat Sheet

 Node.js, Express.js & MongoDB Interview Cheat Sheet

Node.js (Basic)

1. What is Node.js?

- Node.js is a runtime to run JavaScript on the server side.

2. What is the event loop?

- A mechanism that handles asynchronous operations in Node.js.

3. What are callbacks?

- Functions passed to other functions for asynchronous handling.

Example:

fs.readFile('file.txt', (err, data) => { if (err) return; console.log(data.toString()); });

4. Difference between synchronous and asynchronous:

- Sync blocks execution. Async uses callbacks/promises to avoid blocking.

 

Express.js (Basic)

1. What is Express.js?

- A lightweight web framework for Node.js.

2. Creating a basic server:

const express = require('express');

const app = express();

app.get('/', (req, res) => res.send('Hello'));

app.listen(3000);

3. What is middleware?

- Functions executed during request processing.

 

MongoDB (Basic)

1. What is MongoDB?

- A NoSQL database using JSON-like documents.

2. Connecting MongoDB:

mongoose.connect('mongodb://localhost:27017/dbname');

3. CRUD with Mongoose:

const User = mongoose.model('User', new mongoose.Schema({ name: String }));

User.find(); User.findOne(); User.findById();

 

Intermediate Questions

1. Error handling in Express:

app.use((err, req, res, next) => { res.status(500).send('Error') });

2. Route parameters:

app.get('/user/:id', (req, res) => res.send(req.params.id));

3. Embedded vs Reference documents:

- Embedded: nested in document.

- Reference: use ObjectId to reference another collection.

 

Scenario-based Q&A

1. REST API Example:

- POST /users to create, GET /users to read data.

2. CORS in Express:

const cors = require('cors'); app.use(cors());

3. Helmet + Rate Limiting:

app.use(helmet()); app.use(rateLimit({ windowMs: 15*60*1000, max: 100 }));

4. JWT Authentication:

jwt.sign(payload, secret); jwt.verify(token, secret, callback);